It is generally known that many diseases of warm-blooded animals including human and fishes are caused by a virus. For instance, as the diseases caused by such virus which infests an animal as the host, there are mentioned Newcastle disease, chicken pox and infectious bronchitis of fowl; infectious hepatitis of ducks; cholera and infectious gastroenteritis of hogs; pox, foot-and-mouth disease, vesicular stomatitis and para-influenza of cows. In the past, antibiotical substances of the tetracycline type and some vaccines were only occasionally used as the antiviral agent for the therapeutic prevention and/or treatment of several of the above-mentioned viral diseases. Sometimes, however, the antibiotical substances previously used for this purpose involve a problem in that frequent use of the antibiotics would impart the drug-resistance to the pathogenic bacteria, resulting in an increase in the number of antibiotic-resistant bacteria. Vaccines are of delayed action and are active against a limited scope of the viral diseases owing to the inherent nature of the vaccine.
Many viral diseases of fishes are also known. Infectious viral diseases of fishes are progressively increasing in the recent years as artificial cultivation of fishes has spread on a commercial scale. Infectious viral diseases of fishes result in the rapid kill of a large quantity of cultivated fishes and particularly cultivated young fishes and bring about an important damage in the artificial cultivation of fishes. As representative examples of viral diseases of fishes are known infectious pancreas necrosis and infectious necrosis of hematopoietic organs of fishes. These viral diseases frequently attack, for example, rainbow trout, brook trout (Salvelinus fontinalis), landlocked salmon (Oncorhynchus muso var, ishikiwar), red salmon, silver salmon, sook eye salmon and dogsalmon (Oncorhynchus keta). Hithertofore, various methods of preventing and therapeutically treating the viral diseases of fishes have been developed and tested, but such antiviral agents, including vaccines, which are satisfactorily effective for the therapeutic prevention and treatment of the viral diseases of fishes are not yet available.
Many viral diseases of humans are also known, and various methods of preventing and therapeutically treating human viral diseases have been investigated for a long time. As a result, several vaccines, for example, polio-virus vaccine, have been developed, and infection of some of the viral diseases in human is successfully suppressed by the use of vaccines. However, it is to be noted that the number of the vaccines which are effective in clinical practice is still few. Chemotherapeutic, antiviral agents such as iodoxyuridine and 1-admantanamine (known commonly as "Amantadine") are tested for the therapeutic treatment of herpes virus diseases and viral hepatitis where the pathogenic virus usually can replicate for a long period of time even after the development of viral infection, as well as for the therapeutic treatment of influenza where the antigenicity of the virus involved is very likely to vary. No antiviral agent which is effective to prevent and treat therapeutically a wide range of viral diseases is available at present. Infections of common pathogenic bacteria have been greatly reduced by the propagated use of antibiotics in the recent years, but in contrast different viral diseases which have avoided public observation up to now have become the center of public attention at present. For instance, viral diseases such as progressive multifocal leucoencephalopathy, human cytomegalic inclusion disease and acute hemorrhagic conjuctivitis have became new problems in the clinics. Furthermore, it is reported that many of the chronic diseases which are difficult to cure completely by the use of known antibiotics are caused by multiple infections by bacteria and viruses.
We, the present inventors, have made extensive research in an attempt to seek new antiviral agents which have rapid action in the therapeutic treatment of viral diseases and have a wide range of antiviral spectrum. As a result, we have now found that glycine derivatives of the under-mentioned general formula (I) (hereinafter sometime referred to merely as the compound(s) of the present invention) are very highly active against many of the viral infections, and that these glycine derivatives shows substantially no or little toxicity to warm-blooded animals and fishes. The glycine compounds of the general formula (I) are distinct from the normal amino-acids which usually constitute proteins, but are abnormal amino-acids which may be called structural analogues to the aforesaid normal amino-acids.